Zarathustra Spitama (زرتشت Zartosht or زردشت Zardosht in Persian; Ζωροάστρης in Greek; and in Avestan) was an Avestan-speaking Persian who (if he actually existed?) was the author of the Yasna Haptanghaiti and the Gathas, and the spiritual founder of what became known as Zoroastrianism. This was the official religion of Persia from 600 BCE to 650 CE (1250 years!!), but was suppressed by Islamic conquest of Persia from the 7th century. He is traditionally said to have lived from 628-551 BCE, but scholars generally place him much earlier – some time between 1700 and 1300 BCE. It is said (by whom?) to have influenced many other religions, including Christianity, Gnosticism and Islam.
I'm yet to read Also sprach Zarathustra: Ein Buch für Alle und Keinen (Thus Spoke/Spake Zarathustra), a philosophical novel by Nietzsche which contains themes of: eternal recurrence; the "evolution" of humans (towards transhumanism, perhaps?); and the increasing irrelevance/evil of religion ("god is dead"). Sounds like a cracking read!